Electronic chips typically need to be packaged in a package that provides an electric circuit between each electrical connection from the chip and an external connector such as a pin or a ball extending from the package to external circuitry such as a printed-circuit board. The circuitry on the chip, particularly a very fast chip such as a microprocessor, generates a considerable amount of heat. Typically, the circuitry and electrical connections for a chip are provided on one face of the chip. Sometimes, the majority of heat is removed from the opposite face of the chip.
The circuit side of the chip typically provides pads that are connected to the chip's packaging using, for example, solder-ball connections, which provide connections for electrical power and for input-output signals. The opposite, or back, side of the chip can have a heatsink or other heat-removing device attached, providing heat elimination. For some systems, a thermal-interface material (TIM) is used to attach a heat spreader to the back of an IC chip. In some systems a second thermal-interface material is used to attach a heat sink to the heat spreader.
A package for a chip or chips typically has a non-conductive substrate (such as a plastic film or layer, or a ceramic layer) with conductive traces above a surface of the substrate. Package wiring is becoming smaller, multilayered, and denser. Either solder-ball connections or wirebonds connect a chip to the package. Some packages include multiple chips, such as one or more logic or processor chips, one or more communications chips (such as for a cell phone or wireless LAN), and/or one or more memory chips, such as DDR RAMs (double-data-rate random-access memories, which are typically volatile and lose their contents when power is removed) and/or a FLASH-type reprogrammable non-volatile memory. Optionally, a cover or encapsulant is used to enclose parts or all of the chip or chips.